[TowerTalk] Irrigation pipe vertical

[Dan Hearn]

I have made some bushings by cutting hacksaw slots lengthwise on short
pieces of tubing and squeezing it together to insert. I picked up a beam
from the estate of W7BUD which had a piece of 3 inch irrigation tubing about
4 feet long, slit lengthwise and inserted into a longer piece of the same
tubing to strengthen it. This also works well for splicing 2 pieces of
identical tubing together. BUD put some grease on the slotted piece to help
shoving it into place. I suspect he used a piece of wood and a hammer to
drive it into place. He used a sheet metal screw or 2 to keep it in
position.
73, Dan, N5AR

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com]On Behalf Of Red Haines
Sent: Saturday, December 01, 2007 11:10 AM
To: WA3GIN; TowerTalk
Subject: Re: [TowerTalk] Irrigation pipe vertical


Hi, Dave;

I make the bushings from a piece of 3" aluminum  tubing with 1/2" wall
thickness.  I cut off about a 1" length for each bushing.  I turn one
bushing for a sliding fit outside the 2" pipe.  That bushing is fastened
with screws to the inside of a 3" pipe at the top, after inserting the
2" pipe with a bushing on its bottom.  The bushing for the bottom of the
2" pipe is turned for a sliding fit inside the 3" pipe and is fastened
with screws to the 2" pipe.

Sorry, I don't have any photos.  I built all these before I'd even heard
of digital cameras.

By the way, I don't recommend anything longer than a 30' 3" aluminum
pipe for a permanent antenna;  it may fail in the wind.  A better
combination is a shorter length of 3" pipe supporting a section of 2"
pipe supporting a section of 1" pipe.

Guying the thin irrigation pipe will impose downward force and may lead
to a slender column mode of failure.  The guys must be attached to
minimize bowing in a wind.

The aluminum irrigation pipe is not seamless; it is welded.  The
material is of modest strength, not up to the standards of material used
in many commercial antennas.  Though I've used these as base antennas, I
must recommend caution regarding their susceptibility to failure in
strong wind.  Place then where no harm is done if they fail.

At one time, I calculated the permissible wind and the optimum guy
points for such antennas, but I don't have those figures readily
available.  Perhaps someone will look up the material specs and repeat
the appropriate calculations for the group.  I might do that if I get a
round tuit someday.

73 de Red, WOØW

WA3GIN wrote:

> Red,
>
> I'd love to see some pics of your antennas.  I'm thinking of building
> a 4 square for a salt march on my property.  I'm particularly
> interested in the bushing as that would be very slick.
>
> 73,
> dave
> wa3gin
>
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